1. Field of the Invention
This invention relates to a blade driving device for use in cameras. The blade driving device is openably and closably disposed in front of an image pickup element and is capable of shielding an exposure aperture from part or all of light passing through the aperture. The blade driving device is also capable of reducing the light passing therethrough. More particularly, the invention relates to a blade driving device for use in cameras that is mounted on a portable information terminal such as a portable telephone or a portable personal computer.
2. Description of the Related Art
As a conventional digital still camera provided with an image pickup element, such as a CCD (charge coupled device), there is known a camera in which a mechanical shutter blade disposed in front of a CCD opens and closes an optical path. When the camera is in a photographic standby state, the CCD starts storing an electric charge as shown in FIG. 1, in response to a releasing operation while keeping the mechanical shutter blade in an open state. When a predetermined period of exposure time passes, an electromagnetic actuator, such as a motor, is supplied with an electric current for closing and the mechanical shutter blade is controlled to close the exposure aperture (see Japanese Unexamined Patent Publication No. Hei-4-281684, Japanese Unexamined Patent Publication No. Hei-6-70224, and Japanese Unexamined Patent Publication No. Hei-1-310329, for example).
Using the conventional digital still camera, the mechanical shutter blade of the camera is kept in a state of opening the optical path by, for example, a magnetic urging force of the electromagnetic actuator when the camera is in a standby state prior to photography.
A similar mechanical shutter blade can be used in, for example, a mobile camera mounted on a portable telephone or a portable personal computer. In this application, an occasion could arise where the camera receives an external impulsive force or the like caused when the camera is accidentally dropped or is bumped against another object. Additionally, the chance of receiving such an impulsive force will increase if the mobile camera is used more often than a general digital camera.
There could also be a case in which, when such an impulsive force is applied from the outside, the camera is in a photographic standby state. In this state, the shutter blade being in an opened state is freely closed by the impulsive force so that photography cannot be disadvantageously performed.